Method for emphasizing differences in graphical appearance between an original document and a modified document with annotations

ABSTRACT

A method for emphasizing differences in graphical appearances between an original document and a modified document is provided in accordance with an aspect of the present invention. The method includes the step of receiving a first bitmap of the modified document, and a second bitmap of the original document. The method includes deriving a set of difference points based upon a comparison of the first bitmap and the second bitmap. The method includes a step of superposing a spatial index onto the set of difference points, and generating polygon vertices from a plurality of adjacent elements of index. Each of the elements has a predetermined density of difference points. The method concludes with generating an annotation from the polygon vertices.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND

1. Technical Field

The present invention relates generally to methods for electronicdocument revision tracking and control. More particularly, the presentinvention relates to methods for emphasizing differences in graphicalappearance between an original document and a modified document withattached annotations.

2. Related Art

Advancements in high speed data communications and computingcapabilities have increased the use of remote collaboration forconducting business. While real-time collaboration usingvideoconferencing and the like are gaining in popularity, the vastmajority of collaboration occurs over e-mail in the exchange ofdocuments incorporating incremental modifications, comments, and thelike. A local user may create an initial version of a document, andtransmit the same to remotely located colleagues. These remote users maythen make their own changes or add comments in the form of annotationsappended to the document, and then transmit the new version back to thelocal user.

Such collaboration may involve the exchange of documents generated withword processing applications, desktop publishing applications,illustration/graphical image manipulation applications, Computer AidedDesign (CAD) applications, and so forth. As utilized herein, the term“document” may refer to data produced by any of the aforementionedsoftware applications. Furthermore, the term “content” may refer to dataparticular to the software application that generated it and stored inthe document of the same. Due to the existence of many differentcomputing platforms having a wide variety of operating systems,application programs, and processing and graphic display capabilities,however, it has been recognized by those in the art that adevice-independent, resolution-independent file format was necessary tofacilitate such exchange. In response to this need, the PortableDocument Format (PDF), amongst other competing formats, has beendeveloped.

The PDF standard is a combination of a number of technologies, includinga simplified PostScript interpreter subsystem, a font embeddingsubsystem, and a storage subsystem. As those in the art will recognize,PostScript is a page description language for generating the layout andthe graphics of a document. Further, per the requirements of the PDFstorage subsystem, all elements of the document, including text, vectorgraphics, and raster (bitmap) graphics, collectively referred to hereinas graphic elements, are encapsulated into a single file. The graphicelements are not encoded to a specific operating system, softwareapplication, or hardware, but are designed to be rendered in the samemanner regardless of the specificities relating to the system writing orreading such data. The cross-platform capability of PDF aided in itswidespread adoption, and is now a de facto document exchange standard.Currently, PDF is utilized to encode a wide variety of document types,including those composed largely of text, and those composed largely ofvector and raster graphics. Due to its versatility and universality,files in the PDF format are often preferred over more particularizedfile formats of specific applications. As such, documents are frequentlyconverted to the PDF format.

The exchange of documents according to the workflow described above maytake place numerous times, with the content of the document evolvingover time. For example, in various engineering projects utilizing CADdrawings, such as in architecture or product design, a first revision ofthe document may include only a basic outline or schematic. Subsequentrevisions may be generated for review and approval as further featuresor details are added prior to construction or production. On a moreextended timeline, multiple iterations of designs may be produced. Inanother example, an author or a graphics designer may produce an initialdraft of a document, with editors and reviewers adding comments orotherwise marking the document and resubmitting it to the author orgraphics designer. The changes are incorporated into a subsequentversion. While in some instances the review and approval process isperformed directly on the electronic document, there are many instanceswhere a printed hard copy of the document is utilized. As such, thereviewer may annotate, comment upon, or edit the document directly onthe hard copy thereof.

As mentioned briefly above, annotations may be added to a document forcommenting on changes or suggesting changes. The annotations areseparate objects overlaid on the content, and may take a variety offorms such as text, geometric shapes, and the like. Additionalinformation typically accompanies the annotations, such as the date thatit was added to the document, the user who added it, the visual style ofthe annotation, etc. CAD applications such as AutoCAD from AutoDesk ofSan Rafael, Calif., as well as other graphics-oriented applications suchas those for handling PDF documents, include the aforementionedannotation features. One benefit of placing annotations on the documentis that comments and suggested changes may be easily tracked from atabular interface such as that provided by the Revu application fromBluebeam Software, Inc, of Pasadena, Calif.

During collaboration, it is often desirable to review earlier versionsof a document and compare the same to a current version. By doing so,the evolution of the content may be better appreciated, and each changemade to the content may be tracked for approval and other purposes. Assuch, there is a need for software tools that can rapidly andautomatically identify differences between two documents. For example,where the document includes hundreds of pages but a change is made inonly one or two sentences therein, it is difficult to manually searchfor the change within the large volume of text. Further, where anengineering drawing contains numerous details, but where only a singledimension is changed, manually identifying it is very time-consuming.Indeed, such minor changes may have been ignored completely by areviewer, resulting in delays, production defects, and the like.

A number of document comparison techniques are known in the art. WORDfrom Microsoft Corp. of Redmond, Wash., includes a “track changes”function that allows multiple users to review, insert comments, edit,and supplement the content generated by the originator. Anything addedor removed by subsequent users are highlighted with different colors,underlined, the text rendered with strikethroughs, and otherwiseemphasize the difference within the document. As with the textualcontent comparison system of Word, graphical content comparison systemsapply highlights and other emphases directly onto the content, or changecertain attributes of the content. Therefore, the integrity of thecontent is affected. Furthermore, discerning one difference from anotheris difficult, particularly where there are a large number ofdifferences. In the alternative, a separate listing or report ofdifferences is generated, or the highlighting the differences directlyon an output screen. Prior techniques frequently misidentifieddifferences, and are thus deficient. For example, where a border isadded but the content is not modified, the entire area of the border isidentified as a difference along with the unchanged content, renderingthe comparison process ineffective.

Accordingly, there is a need in the art for an improved method forhighlighting graphical appearance differences between an originaldocument and a modified document. More particularly, there is a need inthe art for comparing the original document to the modified document andderiving annotations for appending thereto, such that the changes arequickly and easily identified.

BRIEF SUMMARY

In accordance with one aspect of the present invention, there isdisclosed a method for emphasizing differences in graphical appearancesbetween an original document and a modified document with attachedgraphic objects. In this regard, the integrity of the original contentlayer is not affected. Furthermore, a readily accessible visualrepresentation of the difference is provided. The method may commencewith receiving a first bitmap of the modified document, and a secondbitmap of the original document. Thereafter, the method may continuewith deriving a set of difference points based upon a comparison of thefirst bitmap and the second bitmap. The difference points may berepresentative of coordinates within the first and second bitmaps withpixel value differences that exceed a predetermined threshold. Themethod may also include a step of superposing a spatial index onto theset of difference points. The spatial index may be defined bycontiguously spaced cells bound by cell vertices. Additionally, themethod may include a step of generating polygon vertices from the cellvertices of a plurality of adjacent cells. Each of the adjacent cellsmay have a predetermined density of a subset of the difference points.The method may conclude with generating from the polygon vertices anannotation defined by annotation vertices.

The annotations may be tracked in a list or catalogue, and do not affectthe underlying content. Additionally, such a list can be sorted,filtered and linked with a visual display, with the capability ofchanging its status, posting comments and replies to the annotations,and so forth. The annotations may also be stored, summarized, andexported, substantially improving collaboration.

In accordance with another aspect of the present invention, the methodfor emphasizing differences in graphical appearances between an originaldocument and a modified document may include a step of deriving an outerboundary from a first subset of the polygon vertices. Additionally insuch a method may include the step of assigning the polygon verticesthat define the outer boundary to the annotation vertices. Aftergenerating the polygon vertices, the method may include removinginterior polygon vertices that are located within the outer boundary andsurrounded by neighboring polygon vertices.

The step of deriving an outer boundary may include sequentially storingin an outer trace list each of the first subset of the polygon verticesaround the outer boundary. This may begin with an outer starting point,and continue in a first generally rotational direction. The polygonvertices in the outer trace list may be associated with a first portionof the annotation vertices. After deriving the outer boundary, themethod may include removing each of the polygon vertices lying within asingle contiguous line segment. Additionally, the method may includeremoving central vertices of polygon corners.

According to yet another aspect of the present invention, a method foremphasizing differences in graphical appearances between an originaldocument and a modified document may include a step of deriving an innerboundary. The inner boundary may be derived from one or more groups of asecond subset of the polygon vertices. Thereafter, the polygon verticesthat define the one or more inner boundaries may be assigned to theannotation vertices. After generating the polygon vertices, the methodmay include removing interior polygon vertices. The interior polygonvertices may be located within the outer boundary and the inner boundaryand surrounded by neighboring polygon vertices.

In another aspect of the present invention, the step of deriving theinner boundary may include sequentially storing a first one of thegroups of the second subset of the polygon vertices in an inner tracelist around a first one of the inner boundaries. This step may beginfrom a first inner starting point, and proceed in a second generallyrotational direction. Upon completion, the polygon vertices in the innertrace list may become associated with a second portion of the annotationvertices. Furthermore, the method may include sequentially storing asecond one of the groups of the second subset of the polygon vertices inthe inner trace list. The retrieval of the polygon vertices may proceedin the second generally rotation direction beginning with a second innerstarting point. Upon storing the polygon vertices in the inner tracelist, the method may continue with removing each of the polygon verticeslying within a single contiguous line segment. Additionally, the methodmay include removing central vertices of polygon corners.

According to another aspect of the present invention, the pixel valuedifferences may be related to red, green, and blue luminance values. Thedifference points may be representative of coordinates within the firstand second bitmaps with neighboring pixel value differences that exceeda predetermined threshold. Prior to receiving the first bitmap and thesecond bitmap, the modified document may be converted to the firstbitmap and the original document may be converted to the second bitmap.

Various modalities of presenting the annotated document to the user iswithin the scope of the present invention. According to one aspect, theannotation may be overlaid on the modified document, which is displayedin a graphical user interface. Alternatively, the method may includeoverlaying the annotation on the modified document, with the modifieddocument and the original document being displayed simultaneously in agraphical user interface.

The present invention will be best understood by reference to thefollowing detailed description when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodimentsdisclosed herein will be better understood with respect to the followingdescription and drawings, in which like numbers refer to like partsthroughout, and in which:

FIG. 1 is a perspective view of a computer system that may be used toimplement aspects of the present invention, including a system unit, adisplay unit, and various other input devices;

FIG. 2 is a block diagram of the components of the system unit in thecomputer system illustrated in FIG. 1;

FIG. 3 is an example of an original document including various text andgraphic elements;

FIG. 4 is an example of a modified document with certain text andgraphic elements being different as compared to the original document;

FIG. 5 a is a flowchart describing a method of emphasizing differencesbetween the original document and the modified document with attachedgraphic objects in accordance with an aspect of the present invention;

FIG. 5 b is a method for generating annotations after differencesbetween documents have been identified in accordance with another aspectof the present invention;

FIG. 6 is a block diagram illustrating the various data files andfunctional blocks for implementing the method of emphasizing differencesbetween the original document and the modified document;

FIG. 7 is a view of an exemplary bitmap with sample content, magnifiedto the extend of visualizing individual pixels;

FIG. 8 is a visualization of difference points between the originaldocument and the modified document;

FIG. 9 is a visualization of the difference points with a gridsuperposed thereon in accordance with an aspect of the presentinvention;

FIG. 10 is a visualization of the difference points with a grid aftercertain cells have been removed for lacking a sufficient density ofdifference points thereunder;

FIG. 11 is a first exemplary polygon defined by cell vertices extractedfrom the grid;

FIG. 12 is a visualization of difference points resulting in a secondexemplary polygon including a cavity, with a grid superposed thereon;

FIG. 13 is the second exemplary polygon including polygon vertices;

FIG. 14 a representation of the first polygon with interior polygonvertices removed;

FIG. 15 is a representation of the second polygon with the interiorpolygon vertices removed;

FIG. 16 illustrates an outer boundary of the first polygon being derivedfrom the polygon vertices thereof;

FIG. 17 illustrates an outer boundary of the second polygon beingderived from the polygon vertices thereof;

FIG. 18 a is a first section of a flowchart illustrating the procedureof tracing each of the polygon vertices to derive the outer boundary ofthe first and second polygons;

FIG. 18 b is second section of a flowchart illustrating the procedure oftracing each of the polygon vertices in accordance with an aspect of thepresent invention;

FIG. 18 c is a table containing the order in which the polygon verticesare traced;

FIG. 19 is a series of example polygon vertices for illustrating theprocesses of tracing the boundary of the same in accordance with anaspect of the present invention;

FIG. 20 is a diagram of the second polygon that illustrates the processof inner boundaries being traced, and its relation to tracing the outerboundary;

FIG. 21 depicts the removal of intermediate polygon vertices from thefirst polygon in accordance with an aspect of the present invention;

FIG. 22 depicts the removal of central vertices of inward polygoncorners from the first polygon;

FIG. 23 depicts the removal of central vertices of outward polygoncorners from the second polygon;

FIG. 24 is a screen capture of a graphical user interface that isdisplaying the modified document with annotations overlaid thereon; and

FIG. 25 is a screen capture of the graphical user interface where themodified document including the annotations is displayed simultaneouslywith the original document.

Common reference numerals are used throughout the drawings and thedetailed description to indicate the same elements.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of the presently preferredembodiment of the invention, and is not intended to represent the onlyform in which the present invention may be constructed or utilized. Thedescription sets forth the functions and the sequence of steps fordeveloping and operating the invention in connection with theillustrated embodiment. It is to be understood, however, that the sameor equivalent functions and sequences may be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of the invention. It is further understood that the use ofrelational terms such as first and second, and the like are used solelyto distinguish one from another entity without necessarily requiring orimplying any actual such relationship or order between such entities.

With reference to FIG. 1, an exemplary hardware environment in whichaspects of the present invention may be implemented includes a computersystem 10 with a system unit 12 and a display unit 14. The display unit14 graphically displays output from the data processing operationsperformed by the system unit 12, and may be of a Liquid Crystal Display(LCD) type, a Cathode Ray Tube (CRT) type, or any other suitable type ofdisplay. Devices such as a keyboard 16 and a mouse 18 provide input tothe data processing operations, and are connected to the system unit 10via a USB port 20. Various other input and output devices may beconnected to the system unit 12, and alternative interconnectionmodalities may be substituted with the USB port 20.

As shown in the block diagram of FIG. 2, the system unit 12 includes aCentral Processing Unit (CPU) 22, which may represent one or moreconventional types of such processors, such as an IBM PowerPC, IntelPentium (x86) processors, and so forth. A Random Access Memory (RAM) 24temporarily stores results of the data processing operations performedby the CPU 22, and is interconnected thereto typically via a dedicatedmemory channel 23. The system unit 10 may also include permanent storagedevices such as a hard drive 26, which are also in communication withthe CPU 22 over an i/o bus 27. Other types of storage devices such astape drives, Compact Disc drives, and the like may also be connected. Agraphics card 28 is also connected to the CPU 22 via a video bus 29, andtransmits signals representative of display data to the display 14. Asindicated above, the keyboard 16 and the mouse 18 are connected to thesystem unit 12 over the USB port 20. A USB controller 30 translates dataand instructions to and from the CPU 22 for external peripheralsconnected to the USB port 20. Additional devices such as printers,scanners microphones, speakers, and the like may be connected to thesystem unit 12.

The system unit 12 may utilize any operating system having a graphicaluser interface (GUI), such as WINDOWS from Microsoft Corporation ofRedmond, Wash., MACOS from Apple, Inc. of Cupertino, Calif., variousversions of UNIX with the X-Windows windowing system, and so forth. Thesystem unit 12 executes one or more computer programs, with the resultsthereof being displayed on the display unit 14. Generally, the operatingsystem and the computer programs are tangibly embodied in acomputer-readable medium, e.g. one or more of the fixed and/or removabledata storage devices including the hard drive 26. Both the operatingsystem and the computer programs may be loaded from the aforementioneddata storage devices into the RAM 24 for execution by the CPU 22. Thecomputer programs comprise instructions which, when read and executed bythe CPU 22, cause the same to perform the steps necessary to execute thesteps or features of the present invention.

The foregoing computer system 10 represents only one exemplary apparatussuitable for implementing aspects of the present invention. As such, thecomputer system 10 may have many different configurations andarchitectures. Any such configuration or architecture may be readilysubstituted without departing from the scope of the present invention.

With reference to FIGS. 3 and 4, an aspect of the present inventionrelates to a method for emphasizing differences in graphical appearancesbetween an original document 32 and a modified document 34. In oneembodiment, both the original document 32 and the modified document 34are stored as a Portable Document Format (PDF) file, which, as describedabove, include text, vector graphics, and raster (bitmap) graphics. Byway of example, a heading 36 of the original document 32 is “PlanningDesk,” and includes an illustration of a house with a slanted leftroofline 38. In comparison, the heading 36 of the modified document 34is “Planning”. Furthermore, the roofline 38 has been changed altered. Itis understood that the foregoing graphical elements of the originaldocument 32 and the modified document 34 are presented for exemplarypurposes only. According to an aspect of the present invention, each ofthe aforementioned differences is highlighted for rapidly identifyingthe same.

With reference to the flowchart of FIG. 5 a and the block diagram ofFIG. 6, the method includes a step 200 of receiving a first bitmap 48 ofthe modified document 34, and a second bitmap 50 of the originaldocument 32. As described above, according to one embodiment, theoriginal document 32 and the modified document 34 are PDF files, withthe contents thereof being stored as discrete objects of text andgeometric primitives. Accordingly, the original document 32 is convertedto the second bitmap 50 and the modified document 34 is converted to thefirst bitmap 48 by a converter 52. It is contemplated that the originaldocument 32 and the modified document 34 exist as bitmap files, in whichcase the aforementioned conversion is skipped.

Referring to a magnified area of the original document 32 as shown inFIG. 7, an exemplary bitmap 54 is comprised of rows 56 and columns 58 ofpixels 60. The pixels 60 are arranged to define the letter “T” in theexemplary bitmap 54. Each of the pixels 60 represents one point in theimage, and is particularly referenced by a set of coordinatesidentifying a particular one of the rows 56 and a particular one of thecolumns 58. Further, each of the pixels 60 has associated therewith aset of three luminance values. A first luminance value represents theintensity of the red color, a second luminance value represents theintensity of the green color, and a third luminance value represents theintensity of the blue color. The intensity is represented as a numericalvalue, typically between 0 and 255 for an 8-bit color depth. Bycombining varying intensities of the red, green, and blue colors, anycolor may be represented. Along these lines, the resolution of thebitmap may be varied according to the number of pixels per inch.

In order to account for minor inconsistencies in the bitmaps, a numberof adjustments are made thereto. More particularly, the scale of thebitmap may be adjusted based upon a specified Dots Per Inch (DPI)/PointsPer Inch (PPI) setting. Additionally, the offset may be adjusted basedon a specified offset value. Further preparations for comparing thebitmaps include overwriting the edges of the bitmap based upon a marginsetting. A copy of the respective one of the bitmaps of the originaldocument 32 and the modified document 34 may be stored as a temporaryfile on the hard drive 26 or the RAM 24. For faster access, the bitmapsare locked into the RAM 24.

According to a step 202, the method continues with deriving a set ofdifference points 62 based upon a comparison of the first bitmap 48 andthe second bitmap 50 by a differencer 63. The difference points 62 arerepresentative of pixels within the first and second bitmaps 48, 50having pixel value differences exceeding a predetermined threshold. Moreparticularly, the red, green, and blue luminance values are compared foreach pixel in the first and second bitmaps 48, 50. If the maximumdifference amongst the red, green, and blue components is greater than apredetermined color sensitivity setting, the coordinates for theparticular pixel is retained as one of the difference points 62.

In accordance with another aspect of the present invention, thedifference points 62 are also representative of coordinates within thefirst and second bitmaps 48, 50 with neighboring pixel value differencesexceeding a predetermined threshold. In other words, where a differencein one pixel is identified, each of the neighboring pixels is comparedwith the corresponding one of the pixels in the other bitmap. Again, ifthe maximum difference amongst the red, green, and blue components inthat neighboring pixel is greater than the predetermined colorsensitivity setting, the coordinates of the initial pixel is retained asone of the difference points 62. The extent to which neighboring pixelsare recursively examined in this manner is determined by a proximitysetting. In this regard, documents with high noise/error content may beprocessed differently to avoid false positives as compared to documentswith low noise/error content.

Continuing with the example presented in the original and modifieddocuments 32, 34 of FIGS. 3 and 4, FIG. 8 is a visual representation ofthe difference points 62 derived in accordance with step 202 and asdescribed above. Referring to FIGS. 5 a and 9, the method in accordancewith an aspect of the present invention includes a step 204 ofsuperposing a spatial index or grid 64 on to the set of differencepoints 62. As shown in the block diagram of FIG. 6, a superposer 66receives input in the form of difference points 62 and the grid 64, andgenerates a combined grid/difference point plot 67. A visualrepresentation of the plot 67 is shown in FIG. 9, though only one groupof difference points 62 with the grid 64 overlaid thereon isillustrated. It is to be understood, however, that the grid 64 coversthe entire field of the first or second bitmap 48, 50. The grid 64 isdefined by contiguously spaced cells 68 bound by cell vertices 70 thatare intersection points of gridlines 72. The size of the cells 68 inrelation to the first and second bitmaps 48, 50 is user-defined, thougha default value may be assigned. As will be explained further below, thesize of the cells 68, or the distribution of the gridlines 72, affectsthe resolution and degree of accuracy in identifying differences.

After superposing the grid 64 on to the difference points 62, a step 206of deriving polygon vertices from the cell vertices 70 follows. The cellvertices 70 of a plurality of adjacent cells 68 are utilized, with eachhaving a predetermined density of a subset of the difference points 62disposed within such cells 68. In further detail, the density ofdifference points 62 in each of the cells 68 is determined by a densityprocessor 69, and those cells 68 having a predetermined thresholddensity are retained. Essentially, a histogram of the difference points62 segregated into the cells 68 of the grid 64 is generated. Where agiven one of the cells 68 does not have a sufficient density ofdifference points 62 but has at least one difference point 62 withinthat cell, the density of difference points 62 in each of theneighboring cells 68 are determined. If the neighboring cells 68 have asufficient density, then the one of the cells having at least onedifference point but insufficient density of difference points 62 isretained. In this regard, the cells 68 containing noise are removed,while the cells 68 containing the periphery of legitimate clusters ofdifference points 62 are retained. One of the advantages of processingareas of the bitmap as bounded by the cells 68, as opposed to processingthe individual difference points 62, is that processing efficiency isgreatly enhanced. As will be appreciated, only a couple hundred cells 68need be processed, rather than tens of thousands of individualdifference points. Thus, the size of the cells 68 should be maximizedfor decreasing the number to be processed, but not to the extent ofaffecting the accuracy in which the corresponding annotation covers thedifferences. As each page in a document may dictate a different cellsize, according to an aspect of the present invention, the cell size maybe modified before processing.

With reference to FIG. 10, a visual representation of the active gridlist 74 is shown. Along these lines, there may be more than one group ofcells 68 that have been retained, but with each group being locatedapart from another. As such, the step 206 is also understood toencompass the process of grouping adjacent cells 68 in the active gridlist 74. Generally, a cell grouper 75 performs this process with aninput of the active grid list 74, and outputs cell group lists 78. Thisprocess involves a function that recursively searches adjacent cells 68to determine whether it has been retained. By way of example beginningwith a first cell 68, a first iteration 76 sequentially examines an eastdirection 76 a, a northeast direction 76 b, a north direction 76 c, anorthwest direction 76 d, a west direction 76 e, a southwest direction76 f, a south direction 76 g, and a southeast direction 76 h. Upondetermining that the cell 68 in the upward direction 76 c has asufficient density of the difference points 62, without continuing tothe upper leftward direction 76 f, a second iteration 77 is initiatedwith the examination of an east direction 77 a, continuing on to anortheast direction 77 b, a north direction 77 c, and so forth. Whenevera particular cell has been determined to be associated with a group, itis recorded in one of the cell group lists 78. Although the cell grouplists 78 have been mentioned in the plural, it is understood that thedata contained therein be stored in a single list segregated intomultiple groups.

The step of generating polygon vertices continues with a polygonexpander 80 calculating the coordinates of the cell vertices 70corresponding to the four corners of each of the cells 68 in the cellgroup lists 78. With reference to FIG. 11, the particular cell vertices70 that define a first exemplary polygon 82 are also referred to aspolygon vertices 84.

Referring again to the flowchart of FIG. 5 a and the block diagram ofFIG. 6, the method in accordance with an aspect of the present inventionconcludes with a step 208 of generating an annotation 91 from thepolygon vertices 84 with an annotation generator 93. The step 208typically involves additional processing of the polygon vertices 84,however. Generally, as shown in FIGS. 10 and 11, the first exemplarypolygon 82 may be categorized as having a solid interior, that is, eachof the cells 68 within the bounds of the cell vertices 70 has asufficient density of the difference points 62. In the alternative, asshown in FIG. 12, a second exemplary polygon 86 may be categorized ashaving a hollow interior or cavity 88, in which the cells 68 originallysuperposed on those regions of the cavity 88 have not been retainedaccording to the processes described above because of an insufficiencyin density of the difference points 62 therein. This is most commonwhere a border has been added between the compared documents, but wherecontent within such border has not been modified.

Referring to the flowchart of FIG. 5 b, as a preliminary step 220, thepolygon is classified as having a solid interior or a hollow interior.According to one embodiment, a flag may be set for later processingbased upon a density determination made with respect to the polygonvertices. The number of possible cell vertices for a given rectangularregion is compared against the number of actual cell vertices in thatsame rectangular region. By way of example only and not of limitation,if the ratio is more than 60%, it is deemed to have a hollow interior,and the flag is set. Any other suitable ratio may be substituted withoutdeparting from the scope of the present invention. As an example of thestep 220, with reference to FIG. 11 and the first exemplary polygon 82therein, there are fifteen actual cell vertices 84, and would be a totalof twenty if none had been removed. The ratio is 75%, so it is notflagged because it has a solid interior.

Next, according to a step 222, interior polygon vertices are removed.More particularly, an interior polygon vertex is understood to refer tothose polygon vertices that are internal to the polygon and do notdefine a border of the same. According to one embodiment, thisdetermination is made by querying for the existence of neighboringpolygon vertices in all directions. For example, as shown in FIG. 11, afirst interior polygon vertex 89 has eight neighboring polygon vertices90 a-90 h. In other words, the first interior polygon vertex 89 issurrounded and enclosed by the neighboring polygon vertices 90 a-90 h.Similarly, as shown in FIG. 13, second internal polygon vertices 90 ofthe second exemplary polygon 86, are removed. As will be recognized fromthe illustration, each of the second interior polygon vertices 90 have,as indicated above, neighboring polygon vertices in all directions.FIGS. 14 and 15 show the first and second exemplary polygons 82, 86,respectively, after removing the interior polygon vertices as set forthabove.

It is understood that the first and second polygons 82, 86,respectively, are stored as lists of coordinates corresponding to thepolygon vertices 84 thereof, but in no particular order. In other words,the proper outline of boundaries has not yet been determined. Withreference to the flowchart of FIG. 5 b, the method continues with a step224 of deriving boundaries from the polygon vertices 84 by storing in atrace list at least a subset the polygon vertices. This process isotherwise referred to as “tracing” a boundary.

It is understood that the outer boundary is derived for polygons with asolid interior as well as for polygons with a hollow interior. In thisregard, the process of deriving the outer boundary involves storing thepolygon vertices 84 in an outer trace list. Where the polygon has asolid interior, all of the polygon vertices 84 are traced to derive theouter boundary. In the example shown in FIG. 16, a first outer boundary92 of the first exemplary polygon 82 is derived beginning with astarting vertex 93. Each of the polygon vertices 84 is traversed in aclockwise direction and the coordinates thereof are stored in the outertrace list until reaching the starting vertex 93. However, where thepolygon has a hollow interior, as shown in the example of FIG. 17, afirst subset 85 of all of the polygon vertices 84 are traced to derive asecond outer boundary 94 of the second exemplary polygon 86, with asecond subset 87 of the polygon vertices 84 being traced to derive theinner boundaries. The process begins with a starting vertex 95. Thefirst subset 85 of the polygon vertices 84 are traversed in a clockwisedirection, and the coordinates thereof are stored in the outer tracelist until reaching the starting vertex 95.

With reference to the flowchart of FIG. 18 a and the trace order list ofFIG. 18 c, the process of tracing the polygon vertices 84 begins with aninitial state 250, and utilizes a first variable that stores thedirection from which the current polygon vertex was traced and a secondvariable that stores the current polygon vertex from which furthertracing is conducted. In a first static decision branch 252, it isdetermined whether there is an untraced polygon vertex in the northwarddirection. If there is, the first variable is assigned a value of south,per storage step 254. Otherwise, it is next determined whether there isan untraced polygon vertex in the eastward direction per a second staticdecision branch 256. If there is an untraced polygon vertex in theeastward direction, the first variable is assigned a value of westaccording to a second storage step 258. If not, the process continueswith a third static decision branch 260. Here, it is determined whetherthere is an untraced polygon vertex in the southward direction. If thereis, the first variable is assigned a value of north in storage step 262.If not, it is then determined whether there is an untraced polygonvertex in the westward direction according to a fourth static decisionbranch 264. The first variable is assigned a value of east per fourthstorage step 266, if the fourth static decision branch 264 determinedthat the westward direction had an untraced polygon vertex. If not, theprocess ends 292. After executing one of the first, second, third, andfourth storage operations 254, 258, 262, and 266, the coordinates in thesecond variable are stored in the trace list according to step 268.

With reference to FIG. 18 b, if there are additional untraced points ata decision branch 270, the method continues into a dynamic part in whichthe order of directions to attempt to trace changes depending ondirection from which the current polygon vertex was scanned. Otherwise,the process ends 292. The value stored in the first variable is used tocorrelate to a one of the starting rows 300 a-d in the trace order listof FIG. 18 b. As utilized herein, the term specified row refers to theone of the starting rows 300 a-d correlated to the direction value inthe first variable. In a first dynamic decision branch 272, thedirection in the first column DIR_1 of the specified row is examined todetermine whether there is an untraced polygon vertex. If there is, thedirection in the third column DIR_3 of the specified row is stored inthe first variable according to a storage step 274. Otherwise, per asecond dynamic decision branch 276, the direction in the second columnDIR_2 of the specified row is examined for an untraced polygon vertex.If the decision yields a true result, then the first variable isre-written with the direction in the fourth column DIR_4 of thespecified row per storage step 278. If the decision yields a falseresult, then the direction in the third column DIR_3 is checked for anuntraced polygon vertex according to a third dynamic decision branch280. If there is one, then per storage step 282, the first variable isre-written with the direction in the first column DIR_1 of the specifiedrow. If not, then according to a fourth dynamic decision branch 284 thedirection in the fourth column DIR_4 is examined for an untracedpolygon. If there is, the first variable is re-written with thedirection in the second column DIR_2. Otherwise, the process ends 292.Next, per step 288, the coordinates stored in the second variable aretransferred to the trace list, and incremented to the coordinates of thediscovered untraced polygon vertex. Before continuing on to the nextiteration, per decision branch 290, it is determined whether thestarting point is nearby. If not, the process returns to the decisionbranch 270. If there is, the process ends 292.

With reference to FIG. 19, an example iteration of the foregoing tracingprocess will be described. There is a first polygon vertex 96, also thestarting point 95, and to the north thereof, a second polygon vertex 98.To the west of the polygon vertex 98 is a third polygon vertex 100, andto the north of that is a fourth polygon vertex 102. Beginning with theinitial state 250, the process determines whether there is an untracedvertex to the north per the first static decision branch 252. Since apositive determination is made, the first variable is stored with thedirection south as per storage step 254. Thereafter, the coordinates ofthe first polygon vertex 96 are stored in the trace list per step 268,and the second variable is re-written with the coordinates of thediscovered second polygon vertex 98.

Since there are more untraced points per decision branch 270, theprocess continues into the first dynamic decision branch 272. Asindicated above, the one of the starting rows 300 a-d are correlated tothe direction value stored in the first variable, which is south. Thus,row 300 a in which DIR_1 is south, DIR_2 is west, DIR_3 is north, andDIR_4 is east, is the specified row. The process continues through eachof the first, second and third dynamic decision branches 272, 276, 280,and generates a true result at the fourth dynamic decision branch 284,as the third polygon vertex 100 is to the east. Next, per step 286, thefirst variable is rewritten with DIR_2, which is west. According to step288, the coordinates of the second polygon vertex, as stored in thesecond variable, is written to the trace list. Further, the newlydiscovered fourth polygon vertex 102 is written to the second variable.Because the starting point is not nearby according to a response fromthe decision branch 290, the process returns to the decision branch 270.

There are further additional points to be processed per decision branch270, so the process continues with the first dynamic decision branch272. As mentioned above, the first variable has a value of west, and sorow 300 b in which DIR_1 is west, DIR_2 is north, DIR_3 is east, andDIR_4 is south is the specified row. The process continues through thefirst dynamic decision branch 272 because there is no untraced polygonvertex to the west. However, upon reaching the second dynamic decisionbranch, the fourth polygon vertex 102, which is north of the thirdpolygon vertex 100, is discovered. The first variable is rewritten withsouth, because the direction in column DIR_4 and row 300 b is south. Thecoordinates of the third polygon vertex 100 is written, and the secondvariable is incremented to the coordinates of the fourth polygon vertex102, according to step 288. Upon returning to decision branch 270,because there are no further polygon vertices to be processed, the end292 is reached.

As can be seen, the above-described tracing of the outer boundary 94proceeds in a generally clockwise direction. It will be understood bythose of ordinary skill in the art that a counter-clockwise directionmay be readily substituted by changing the order of the first, second,third, and fourth decision branches 232, 234, 236, and 238.

The step 224 of tracing the boundary is also understood to encompass theprocessing of inner boundaries. Where the aforementioned flag is set,indicating that the polygon to which it pertains is hollow, the derivingof the inner boundaries begins. As indicated above, the inner boundariesare derived from a second subset of the polygon vertices 84. Wheremultiple sections of inner boundaries exist, multiple groups of theaforementioned second subset of the polygon vertices 84 are processed.

As explained above, the process of deriving the outer boundary 94 of thesecond polygon 86 concludes upon returning to the starting point 95.With reference to the example of FIG. 20, deriving a first innerboundary 104 begins with identifying the polygon vertices 84 of both thefirst subset 85 (relating to the outer boundary 94) and the secondsubset 87 (relating to the first inner boundary 104) that define theshortest distance between the two. More particularly, each of thepolygon vertices 84 in the first subset 85 are traversed, calculatingthe distance to the nearest untraced polygon vertex of the first group87 a of second subset 87. In the example, these points are identified asa first outer cavity junction point 106, and a first inner cavityjunction point 108, which are stored for future reference. Forefficiency purposes, where a distance of less than two grid-lengths, orstandard distances between two of the polygon vertices 84, has beenencountered during the traversal of the polygon vertices 84 in the firstsubset 85, no others are traversed.

Upon the identification of the first inner cavity junction point 108,each of the polygon vertices 84 associated with the first group 87 a ofthe second subset 87 is traced to derive the first inner boundary 104.This process is almost identical to that described above in relation toidentifying the second outer boundary 94, except the coordinates of thetraced polygon vertices 84 are stored in an inner trace list, and thetrace proceeds in a counter-clockwise direction, as opposed to aclockwise direction as described above in relation to tracing an outerboundary, to ensure that the cavity 88 is not filled.

In order to derive a second inner boundary 105, the remaining polygonvertices 84 of the first subset (relating to the outer boundary 94) andthe second subset 87 of the polygon vertices 84 that define the shortestdistance between the two is identified. The remaining polygon vertices84 in the first subset 85 are traversed as above, with the distance tothe nearest untraced polygon vertex of the second group 87 b of thesecond subset 87 being calculated. In the example, a second outer cavityjunction point 110 and a second inner cavity junction point 112 areidentified. As described above, each of the polygon vertices 84 in thesecond group 87 b of the second subset 87 are traced in acounter-clockwise direction, the coordinates thereof being stored in theinner trace list. The coordinates of the second outer and inner cavityJunction points 110, 112 are stored for later reference.

With reference back to the flowchart of FIG. 5 b, per step 226, theintermediate polygon vertices are removed. As understood, anintermediate polygon vertex is any polygon vertex lying within a singlecontiguous line segment that defines a boundary of the polygon. Forexample, as shown in FIG. 21, a continuous line segment 114 defines thefirst outer boundary 92 of the first exemplary polygon 82, and includessegment polygon vertices 116 a, 116 b, 116 c, and 116 d. The beginningof the continuous line segment 114 is defined by the segment polygonvertex 116 a, while the ending is defined by the segment polygon vertex116 d. It will be appreciated that the intermediate polygon vertices,the segment polygon vertices 116 b and 116 c, do not contribute to theshape of the polygon 82, and slows down the processing of anyannotations generated therefrom. Accordingly, the segment polygonvertices 116 b and 116 c are removed, as are the other polygon vertices84 that have similar characteristics as described above. Referring toFIG. 20, it will be appreciated that regardless of the first and secondouter cavity junction points 106, 110 being intermediate polygonvertices, these are not removed as such points are needed for properlydefining and connecting the second polygon 86 to the cavities 88. Itwill also be appreciated that if the first and second inner cavityjunction points 108, 112 are intermediate polygon vertices, these willnot be removed for the same reason.

After removing the intermediate polygon vertices, central vertices ofpolygon corners are removed for smoothing the same such thatcorresponding annotations cover a sufficient area. For the outerboundaries, the inner corners are removed, while for inner boundaries,outer corners are removed. Unless otherwise noted, the usage of the term“corner” is understood to refer to both outer corners and inner corners.FIG. 22 shows the first exemplary polygon 82 including a first innercorner 120, a second inner corner 122, and a third inner corner 124. Asgenerally understood, inner corners refer to those portions of the firstpolygon 82 that are concave with respect to the exterior thereof. Thecentral vertices of polygon corners are determined by examining thedirection of adjoining polygon vertices 84, and retrieving the remainingpolygon vertices 84 to determine whether others exist on a straight linein the opposite direction from the adjoining polygon vertices 84.Returning to the example of FIG. 22, the first inner corner 120 isdefined by a beginning vertex 126, an ending vertex 128, and centralvertices 130 a, 130 b, and 130 c. By removing the central vertices 130a-c, the outer boundary 92 extends directly from the beginning vertex126 to the ending vertex 128. Along these lines, a central vertex 132 ofthe second inner corner is removed, as is a central vertex 134 of thethird inner corner 134. FIG. 23 shows the first inner boundary 104 ofthe second exemplary polygon 86 defining the cavity 88. There is a firstouter corner 136 defined by a first central vertex 137 and a secondouter corner 138 defined by a second central vertex 139. Both first andsecond central vertices 137, 139 are identified and removed in the samemanner as described above. It will be appreciated that the coverage ofthe annotation is increased by removing the central vertices 137, 139.

Referring to FIG. 5 b, the process of generating the annotationconcludes with a step 229 of assigning the values of the polygonvertices defining the outer boundaries and the inner boundaries, asapplicable to the vertices that define the visual appearance of theannotation. In the particular example of the second polygon 86, it isunderstood that the first outer and inner cavity junction points 106,108and the second outer and inner cavity junction points 110, 112 serve toconnect the inner boundaries 104, 105 to the outer boundary 94. Asunderstood, annotations may have a variety of parameters that affect thevisual appearance thereof upon rendering, which may applied to theannotation during generation. By way of example only and not oflimitation, the annotation may be assigned a subject, a line and fillcolor, opacity, line stylization, locking parameters, and so forth.

According to another aspect of the present invention illustrated inFIGS. 24 and 25, there are provided various ways of presenting theannotations to the user for rapid identification of differences. Forexample, in FIG. 24, the annotations 150 are overlaid in the modifieddocument 34, which is displayed in a conventional graphical userinterface 152. In another example as shown in FIG. 25, the annotations150 are overlaid on the modified document 34, with the modified documentand the original document 32 being displayed simultaneously in thegraphical user interface 152. Further, it is contemplated that the viewof the modified document 34 and the original document 32 issynchronized, that is, when one of the modified or original documents32, 34 is magnified or panned as shown in the example of FIG. 25, theother document magnifies and pans to the same extent. Other userinterface enhancements known in the art may be readily substitutedwithout departing from the scope of the present invention.

The particulars shown herein are by way of example and for purposes ofillustrative discussion of the embodiments of the present invention onlyand are presented in the cause of providing what is believed to be themost useful and readily understood description of the principles andconceptual aspects of the present invention. In this regard, no attemptis made to show any more detail than is necessary for the fundamentalunderstanding of the present invention, the description taken with thedrawings making apparent to those skilled in the art how the severalforms of the present invention may be embodied in practice.

1. A method for emphasizing differences in graphical appearances betweenan original document and a modified document with attached annotations,the method comprising: receiving a first bitmap of the modified documentand a second bitmap of the original document; deriving a set ofdifference points based upon a comparison of the first bitmap and thesecond bitmap, the difference points being representative of coordinateswithin the first and second bitmaps having pixel value differencesexceeding a predetermined threshold; superposing a spatial index on tothe set of difference points, the spatial index being defined bycontiguously spaced cells bound by cell vertices; generating polygonvertices from the cell vertices of a plurality of adjacent cells eachhaving a predetermined density of a subset of the difference pointsassociated therewith; and generating from the polygon vertices anannotation defined by annotation vertices.
 2. The method of claim 1,wherein the step of generating the annotation further includes: derivingan outer boundary from a first subset of the polygon vertices; andassigning the polygon vertices defining the outer boundary to theannotation vertices.
 3. The method of claim 2, wherein after generatingthe polygon vertices, the method further includes: removing interiorpolygon vertices, the interior polygon vertices being located within theouter boundary and surrounded by neighboring polygon vertices.
 4. Themethod of claim 2, wherein deriving the outer boundary from the firstsubset of the polygon vertices includes: sequentially storing in anouter trace list each of the first subset of the polygon vertices aroundthe outer boundary from an outer starting point in a first generallyrotational direction, the polygon vertices in the outer trace list beingassociated with a first portion of the annotation vertices.
 5. Themethod of claim 2, further comprising: removing each of the polygonvertices lying within a single contiguous line segment defining theouter boundary; and removing central vertices of polygon corners.
 6. Themethod of claim 2, wherein the step of generating the annotation furtherincludes: deriving an inner boundary from one or more groups of a secondsubset of the polygon vertices; and assigning the polygon verticesdefining the one or more inner boundaries to the annotation vertices. 7.The method of claim 6, wherein after generating the polygon vertices,the method further includes: removing interior polygon vertices, theinterior polygon vertices located within the outer boundary and theinner boundary and surrounded by neighboring polygon vertices.
 8. Themethod of claim 6, wherein deriving the inner boundary from one or moregroups of the second subset of the polygon vertices includes:sequentially storing in an inner trace list a first one of the groups ofthe second subset of the polygon vertices around a first one of theinner boundaries from a first inner starting point in a second generallyrotational direction, the polygon vertices in the inner trace list beingassociated with a second portion of the annotation vertices.
 9. Themethod of claim 6, wherein deriving the inner boundary from one of thegroups of the second subset of the polygon vertices includes:sequentially storing in the inner trace list a second one of the groupsof the second subset of the polygon vertices around a second one of theinner boundaries from a second inner starting point in the secondgenerally rotational direction.
 10. The method of claim 6, furthercomprising: removing each of the polygon vertices lying within a singlecontiguous line segment defining a one of the outer boundary and theinner boundary; and removing central vertices of polygon corners. 11.The method of claim 1, wherein the pixel value differences relate tored, green, and blue luminance values.
 12. The method of claim 1,wherein the difference points are representative of coordinates withinthe first and second bitmaps having neighboring pixel value differencesexceeding a predetermined threshold.
 13. The method of claim 1, furthercomprising: converting the modified document to the first bitmaprepresentative of the modified document and the original document to asecond bitmap representative of the original document.
 14. The method ofclaim 1, further comprising: overlaying the annotation on the modifieddocument, the modified document being displayed in a graphical userinterface.
 15. The method of claim 1, further comprising: overlaying theannotation on the modified document, the modified document and theoriginal document being displayed simultaneously in a graphical userinterface.
 16. A method for emphasizing differences in graphicalappearances between an original document and a modified document withattached annotations, the method comprising: receiving a first bitmap ofthe modified document and a second bitmap of the original document;deriving a set of difference points based upon a comparison of the firstbitmap and the second bitmap, the difference points being representativeof coordinates within the first and second bitmaps having pixel valuedifferences exceeding a predetermined threshold; deriving from the setof difference points an outer boundary defined by a first subset ofpolygon vertices; deriving from the set of difference points one or moreinner boundaries defined by one or more groups of a second subset of thepolygon vertices; and generating an annotation defined by an areabetween the outer boundary and the one or more inner boundaries.
 17. Themethod of claim 16, further comprising: removing interior polygonvertices, the interior polygon vertices being located within the outerboundary and the inner boundary, and being surrounded by neighboringpolygon vertices.
 18. The method of claim 16, wherein deriving the firstsubset of the polygon vertices includes: sequentially storing in anouter trace list each of the first subset of the polygon vertices aroundthe outer boundary from an outer starting point in a first generallyrotational direction, the polygon vertices in the outer trace list atleast partially defining the annotation.
 19. The method of claim 16,wherein deriving a first one of the groups of the second sorted subsetof the polygon vertices includes: sequentially storing in an inner tracelist a first one of the groups of the second subset of the polygonvertices around a first one of the inner boundaries from a first innerstarting point in a second generally rotational direction, the polygonvertices in the inner trace list at least partially defining theannotation.
 20. The method of claim 19, wherein deriving a second one ofthe groups of the second sorted subset of the polygon vertices includes:sequentially storing in the inner trace list a second one of the groupsof the second subset of the polygon vertices around a second one of theinner boundaries from a second inner starting point in the secondgenerally rotational direction.
 21. The method of claim 16, furthercomprising: superposing a spatial index on to the set of differencepoints, the spatial index being defined by contiguously spaced cellsbound by cell vertices; and generating polygon vertices from the cellvertices of a plurality of adjacent cells each having a predetermineddensity of a subset of the difference points associated therewith. 22.The method of claim 16, further comprising: removing each of the polygonvertices lying within a single contiguous line segment defining a one ofthe outer boundary and the inner boundary; and removing central verticesof polygon corners.
 23. The method of claim 16, wherein the pixel valuedifferences relate to red, green, and blue luminance values.
 24. Themethod of claim 16, wherein the difference points are representative ofcoordinates within the bitmaps having neighboring pixel valuedifferences exceeding a predetermined threshold.
 25. The method of claim16, further comprising: converting the modified document to the firstbitmap representative of the modified document and the original documentto a second bitmap representative of the original document.
 26. Themethod of claim 16, further comprising the step of: overlaying theannotation on the modified document, the modified document beingdisplayed in a graphical user interface.
 27. The method of claim 16,further comprising the step of: overlaying the annotation on themodified document, the modified document and the original document beingdisplayed simultaneously in a graphical user interface.